Second battery control circuit

ABSTRACT

According to the present invention, there is provided a secondary battery control circuit which can perform a reliable charge/discharge control without activating Positive Temperature Coefficient element. The secondary battery control circuit includes a temperature detection section for detecting a temperature of the secondary battery and a system logic for controlling charging/discharging of the secondary battery based on the temperature detected by the temperature detection section. The system logic interrupts the charging of the secondary battery in a case where the temperature detected by the temperature detection section is out of a predetermined first temperature range, and interrupts the discharging of the secondary battery in a case where the temperature detected by the temperature detection section is out of a predetermined second temperature range.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of and claims benefit priorityto U.S. Non-Provisional patent application Ser. No. 09/700,583, whichapplication is hereby incorporated by reference.

TECHNICAL FIELD

[0002] The present invention relates to a secondary battery controlcircuit, and specifically, to a control circuit for reliably performingthe charging and discharging of a lithium ion secondary battery.

BACKGROUND OF INVENTION

[0003] In the past, as controls for the charging of a lithium ionsecondary battery, a charging voltage control, a charging currentcontrol, a control which enables the charging only within apredetermined temperature range, and the like, have been incorporated ina battery charger. In a battery pack in which a lithium ion secondarybattery, etc., is incorporated, a control which detects the voltage of abattery and interrupts the charging when the voltage is equal to orgreater than a predetermined voltage value is provided as a provisionfor the case where charging voltage control does not work. Theabove-described charging interruption control provided in the batterypack is termed as overcharge protection.

[0004] Furthermore, a control has been performed in which thetemperature of a battery in the above-described battery pack is measuredby a thermistor, an output of which is connected to a battery charger,and in the battery charger, the charging is enabled only within apredetermined temperature range.

[0005] On the other hand, conventionally, as the control associated withthe discharging of the lithium ion secondary battery, etc., a controlwhich interrupts the discharging when a load short-circuit occurs, acontrol which detects an excessive rush current during the dischargingand interrupts the discharging, and a control which detects a constantcurrent during the discharging and interrupts the discharging have beenperformed. These controls are generically referred to as an overcurrentprotection.

[0006] Controls at the battery pack side, such as the above-describedovercharge protection, the thermistor control, and the overcurrentprotection, are generically referred to as safety circuits.

[0007] The above-described overcurrent protection is one of theprotection functions for a battery such as a lithium ion secondarybattery, etc. However, in many cases, in preparation for a case wherethis protection does not work, a PTC element having a ring shape isinstalled in the lithium ion secondary battery itself, or a PTC elementis provided in the battery pack.

[0008] The PTC (Positive Temperature Coefficient) element is an elementsuch that the resistance value is low during a normal operation, butabruptly increases when heated by itself or by an ambient temperature.This element has been used for overcurrent/heatup protection.

[0009] A battery pack which uses a lithium ion secondary battery and thesecondary battery control circuit (safety circuit) is described in, forexample, Japanese Laid-Open Publication No. 10-275612.

[0010] However, in the above-described conventional structure, in thecase where a PTC element having a ring shape which has been installed ina lithium ion secondary battery itself is activated, an expansion forcein a direction of the thickness of the PTC element is affected in adirection in which a caulking portion of a battery sealing portion isopened. This has been a cause for leakage of electrolytic solution.Furthermore, there has been a concern that the deterioration in a lifecycle or the swelling of the secondary battery which results from thefully-charged lithium ion secondary battery, etc., being left in a hightemperature condition.

[0011] Furthermore, there has been a concern that circuit malfunction,corrosion, or problems due to hydrofluoric acid generated by addingwater to an electrolytic solution may be caused in the case where aliquid infiltrates into a secondary battery such as a lithium ionsecondary battery or into a battery pack in which the above-describedsecondary battery is installed, or in the case where an electrolyticsolution inside the battery is leaked.

[0012] In general, the main component of an electrolytic solution whichis used for a lithium ion secondary battery is lithiumhexafluorophosphate.

[0013] The chemical reaction caused in the case where water isinfiltrated into lithium hexafluorophosphate is represented byexpression (1-1). By this chemical reaction, hydrofluoric acid (i.e., avery strong acid) is generated.

LiPOF₆ (lithium hexafluorophosphate)+H₂O→LiPOF₄2HF (water ispresent)→LiF+POF₃↑+2HF↑(after decomposition)  (1-1)

[0014] The present invention solves such conventional problems. Anobjective of the present invention is to provide a secondary batterycontrol circuit which can reliably control charging/discharging withoutactivating a PTC element, which reduces deterioration in life cycle andthe occurrence of swelling of the battery, and which can be installed ina small space section in a battery pack.

SUMMARY OF INVENTION

[0015] In order to achieve a solution to the above problem, a secondarybattery control circuit of the present invention includes: a temperaturedetection section for detecting a temperature of a secondary battery;and a control section for controlling charging/discharging of thesecondary battery based on a temperature detected by the temperaturedetection section, wherein the control section interrupts charging ofthe secondary battery in a case where the temperature detected by thetemperature detection section is out of a predetermined firsttemperature range, and interrupts discharging of the secondary batteryin the case where the temperature detected by the temperature detectionsection is out of a predetermined second temperature range. Thus, aliquid leakage phenomenon of an electrolytic solution due to theactivation of a ring-shaped PTC element installed in a lithium ionsecondary battery itself can be prevented.

[0016] The predetermined second temperature range may include thepredetermined first temperature range.

[0017] A secondary battery control circuit of the present inventionincludes: a voltage detection section for detecting a voltage of asecondary battery; a temperature detection section for detecting atemperature of the secondary battery; and a control section forcontrolling charging/discharging of the secondary battery based on avoltage detected by the voltage detection section and a temperaturedetected by the temperature detection section, wherein in a case wherethe voltage detected by the voltage detection section is equal to orgreater than a predetermined first voltage value, and the temperaturedetected by the temperature detection section is equal to or greaterthan a predetermined temperature, the control section discharges thesecondary battery until the voltage of the secondary battery reaches apredetermined second voltage value. Thus, the deterioration in lifecycle and swelling of the battery which result from a fully-chargedsecondary battery, such as a lithium ion secondary battery, etc., beingleft in a high temperature condition can be prevented.

[0018] It is preferable that the predetermined first voltage value andthe predetermined second voltage value are detected by a single circuithaving a hysteresis.

[0019] It is preferable that either the predetermined first voltagevalue or the predetermined second voltage value is equal to anovercharge releasing voltage value.

[0020] A discharge canceling condition for the secondary battery mayinclude a temperature condition for the secondary battery.

[0021] A secondary battery control circuit of the present inventionincludes a control section for interrupting charging/discharging of thesecondary battery in the case where a liquid is detected by a liquiddetection section for detecting infiltration or generation of a liquidinside the secondary battery or inside a battery pack in which thesecondary battery is installed. In such a structure, when circuitmalfunction, corrosion, or problems due to hydrofluoric acid generatedby adding water to an electrolytic solution (which may be caused in thecase where a liquid is infiltrated into a secondary battery such as alithium ion secondary battery or into a battery pack in which theabove-described secondary battery is installed, or in the case where anelectrolytic solution inside the battery is leaked) are caused, thecharging/discharging of the secondary battery is disabled, whereby auser can be notified of the occurrence of a problem.

[0022] The secondary battery control circuit further includes atemperature detection section for detecting a temperature of thesecondary battery, and the control section may controlcharging/discharging of the secondary battery based on a temperaturedetected by the temperature detection section.

[0023] In the case where the secondary battery control circuit is formedon a single semiconductor chip, a small sized secondary battery controlcircuit is achieved. By enclosing the semiconductor chip in a sealingsection of the secondary battery or by mounting the semiconductor chipin a narrow space section of a battery pack, a secondary battery inwhich a secondary battery control circuit is installed or a small sizedsecondary battery pack in which a secondary battery control circuit ismounted in a narrow space section of, battery pack can be provided.

[0024] Hereinafter, functions of the present invention are described.

[0025] According to one aspect of the invention, in the case where atemperature detected by a temperature detection section is out of apredetermined first temperature range or out of a predetermined secondtemperature range, charging/discharging of the secondary battery isinterrupted. This prevents a liquid leakage phenomenon of anelectrolytic solution due to the activation of a PTC element installedin the secondary battery.

[0026] According to another aspect of the invention, in the case where avoltage detected by a voltage detection section is equal to or greaterthan a predetermined third first voltage value, and the temperaturedetected by a temperature detection section is equal to or greater thana predetermined fourth temperature, the secondary battery is dischargeduntil the voltage of the secondary battery reaches a predeterminedsecond voltage value which is smaller than the predetermined firstvoltage value. By such a forced discharge, deterioration in the lifecycle and swelling of the secondary battery due to the charged secondarybattery being in the high temperature condition can be prevented.

[0027] According to yet another aspect of the invention, in the casewhere the generation of a liquid is detected by a liquid detectionsection, charging/discharging of the secondary battery is interrupted.This allows a user to notice a malfunction or a corrosion or a circuitdue to a liquid, such as water or an electrolytic solution, etc., or aproblem caused due to hydrofluoric acid being generated by addition ofwater to an electrolytic solution.

BRIEF DESCRIPTION OF DRAWINGS

[0028]FIG. 1 is a drawing which shows a configuration of a controlcircuit 20 of a secondary battery 10 according to an embodiment of thepresent invention.

[0029]FIG. 2 is a drawing which shows a relationship between a detectedtemperature and logic levels of output signals O_(T1)-O_(T5).

[0030]FIG. 3 is a drawing which shows a relationship between a detectedtemperature T_(b) and logic levels of a charge disabling signal CD and adischarge disabling signal DD.

[0031]FIG. 4 is a drawing which shows a configuration example of aliquid detection section 62.

[0032]FIG. 5 is a drawing which shows a relationship between ranges fora detected voltage and logic levels of output signals O_(V1)-O_(V6).

[0033]FIG. 6 is a drawing which shows a configuration of a portion of avoltage detecting/outputting section 48 which outputs the output signalO_(V6).

[0034]FIG. 7 is a cross-sectional view which shows a sealing section 80of the secondary battery 10.

DETAILED DESCRIPTION

[0035] Hereinafter, an embodiment of the present invention will bedescribed with reference to the drawings.

[0036]FIG. 1 shows a configuration of a control circuit 20 of asecondary battery 10 (hereinafter, referred to as a secondary batterycontrol circuit 20) according to an embodiment of the present invention.The secondary battery 10 is, for example, a lithium ion secondarybattery.

[0037] The secondary battery control circuit 20 is formed on asemiconductor chip 20 a. In FIG. 1, an area encompassed by a dotted linedenotes an area occupied by the secondary battery control circuit 20formed on the semiconductor chip 20 a. The secondary battery controlcircuit 20 is provided with a positive (+) terminal 22, a negative (−)terminal 24, and a B+ terminal 26.

[0038] The secondary battery 10 is connected between the negative (−)terminal 24 and the B+ terminal 26. A PTC element 12 is connected inseries with the secondary battery 10.

[0039] A battery charger (not shown) or a load (not shown) can beconnected between the positive (+) terminal 22 and the negative (−)terminal 24.

[0040] A FET 30 is provided between the positive (+) terminal 22 and theB+ terminal 26. The FET 30 is a type of switching element that isswitchable among four states based on a gate voltage. A function and anoperation of the FET 30 are equivalent to, for example, a function andan operation of a FET switching element mounted on a semiconductor chipnamed UCC3911 commercially available from UNITRODE Co. The function andthe operation of this switching element are disclosed in U.S. Pat. No.5,581,170.

[0041] The four states of the FET 30 are switched in response to anoutput from a switch (SW) 32 or an output from a charge/dischargecontrol section 42. The four states of the FET 30 are as shown below.

[0042] On state: the secondary battery 10 is chargeable anddischargeable.

[0043] Off state: the secondary battery 10 is not chargeable ordischargeable.

[0044] Intermediate state 1: the secondary battery 10 is chargeable butis not dischargeable.

[0045] Intermediate state 2: the secondary battery 10 is not chargeablebut is dischargeable.

[0046] The secondary battery control circuit 20 controls thecharging/discharging of the secondary battery 10 by controlling thestate of the FET 30. Hereinafter, how the secondary battery controlcircuit 20 controls the FET 30 will be described in detail.

[0047] A temperature detection section 52 detects the temperature of thesecondary battery 10. The temperature detection section 52 and thesecondary battery 10 are thermally coupled by, for example, a metalplate, silicone, etc. The temperature detection section 52 can utilize,for example, a temperature characteristic of a semiconductor. Thetemperature detection section 52 outputs an analog signal indicative ofa detected temperature. The analog signal is supplied to a temperaturestate output section 54.

[0048] The temperature state output section 54 outputs an output signal(O_(T1)-O_(T4)) corresponding to the detected temperature to a systemlogic 46, and outputs an output signal O_(T5) corresponding to thedetected temperature to a forced discharge logic 56. To the temperaturestate output section 54, a reference voltage is supplied from areference voltage generation section 50.

[0049]FIG. 2 shows a relationship between a detected temperature and thelogic levels of output signals O_(T1)-O_(T5). In the case where thedetected temperature is denoted by T_(b) the logic levels of outputsignals O_(T1)-O_(T5) are defined as below:Output signal O_(T1): whenT_(b)<3° C., H level; otherwise, L level.

[0050] Output signal O_(T2): when 3° C.≦T_(b)≦47° C., H level;otherwise, L level.

[0051] Output signal O_(T3): when 47° C.<T_(b)≦95° C., H level;otherwise, L level.

[0052] Output signal O_(T4): when 95° C.<T_(b), H level; otherwise, Llevel.

[0053] Output signal O_(T5): when 35° C.≦T_(b), H level; otherwise, Llevel.

[0054] It should be noted that the temperature ranges shown in FIG. 2are merely examples, and that the present invention is not limited tothe temperature ranges shown in FIG. 2.

[0055] The system logic 46 receives the above-described output signalsO_(T1)-O_(T4), and determines which of the output signals O_(T1)-O_(T4)is at a H level, thereby determining which of a plurality of temperatureranges (i.e., temperature ranges I-VI shown below) the detectedtemperature T_(b) is in. Herein, the temperature ranges I-VI are definedas:

[0056] Temperature range 1: T_(b)<3° C.

[0057] Temperature range II: 3° C.≦T_(b)≦47° C.

[0058] Temperature range III: 47° C.<T_(b)≦95° C.

[0059] Temperature range IV: 95° C.<T_(b)

[0060] Temperature range V: T_(b)<35° C.

[0061] Temperature range VI: 35° C.<T_(b)

[0062] In the case where the detected temperature T_(b) is within thetemperature range II, the system logic 46 sets a charge disabling signalCD to a H level; in the case where the detected temperature T_(b) iswithin the temperature range I, III, or IV, the system logic 46 sets thecharge disabling signal CD to a L level. Herein, the charge disablingsignal CD being at a H level means that charging of the secondarybattery 10 is allowed; the charge disabling signal CD being at a L levelmeans that charging of the secondary battery 10 is prohibited.

[0063] In the case where the detected temperature T_(b) is within thetemperature range I, II, or III, the system logic 46 sets a dischargedisabling signal DD to a H level; in the case where the detectedtemperature T_(b) is within the temperature range IV, the system logic46 sets the discharge disabling signal DD to a L level. Herein, thedischarge disabling signal DD being at a H level means that discharge ofthe secondary battery 10 is allowed; the discharge disabling signal DDbeing at a L level means that discharge of the secondary battery 10 isprohibited.

[0064]FIG. 3 shows a relationship between the detected temperature T_(b)and the logic levels of the charge disabling signal CD and the dischargedisabling signal DD. The charge disabling signal CD and the dischargedisabling signal DD are output from the system logic 46, and aresupplied to the charge/discharge control section 42. Furthermore; FIG. 3also shows a relationship between the detected temperature T_(b) and thelogic level of the output signal O_(T5).

[0065] In response to the charge disabling signal CD at a H level andthe discharge disabling signal DD at a H level, the charge/dischargecontrol section 42 sets the state of the FET 30 to the “ON state”.Similarly, in response to the charge disabling signal CD at a L leveland the discharge disabling signal DD at a L level, the charge/dischargecontrol section 42 sets the state of the FET 30 to the “OFF state”; inresponse to the charge disabling signal CD at a H level and thedischarge disabling signal DD at a L level, the charge/discharge controlsection 42 sets the state of the FET 30 to the “Intermediate state 1”;in response to the charge disabling signal CD at a L level and thedischarge disabling signal DD at a H level, the charge/discharge controlsection 42 sets the state of the FET 30 to the “Intermediate state 2”.

[0066] The operation of a charge pump 44 is controlled by a controlsignal Off output from the system logic 46.

[0067] In this way, in the case where the detected temperature T_(b) isnot within the temperature range II, the charge/discharge controlsection 42 controls the FET 30 so as to interrupt the charging of thesecondary battery 10. In the case where the detected temperature T_(b)is not within the temperature range I, II, or III, the charge/dischargecontrol section 42 controls the FET 30 so as to interrupt thedischarging of the secondary battery 10. The discharging of thesecondary battery 10 is interrupted when the detected temperature T_(b)is not within the temperature range I, II, or III, whereby the secondarybattery 10 can be controlled so that the secondary battery 10 is notdischarged when the detected temperature T_(b) is within the temperaturerange in which an adverse effect can be caused to the PTC element 12. Asa result, the safety in charging/discharging the secondary battery 10can be improved.

[0068] The secondary battery control circuit 20 further includes a WETterminal 28. As shown in FIG. 1, a detected pattern 72 is connected to aliquid detection section 62 through the WET terminal 28. A B+input/output pattern 74 is provided adjacent to the detected pattern 72.The B+ input/output pattern 74 is connected to the B+ terminal 26. Thedetected pattern 72 and the B+ input/output pattern 74 are in closeproximity so that the distance therebetween is about 0.1 mm, but areelectrically separated. Thus, in a normal state, the impedance(resistance value) between the detected pattern 72 and the B+input/output pattern 74 is a value approaching infinity.

[0069] The attachment of a liquid 76, such as water, an electrolyticsolution, etc., reduces the impedance (resistance value) between thedetected pattern 72 and the B+ input/output pattern 74 to several tensto several hundreds of kilo-Ohms. By detecting the reduction in thisimpedance (resistance value), the liquid detection section 62 detectsinfiltration or generation of the liquid in the secondary battery 10 orin a battery pack in which the secondary battery 10 is installed. Forexample, in the case where the secondary battery control circuit 20 ismounted on a printed circuit board, the detected pattern 72 and theB+input/output pattern 74 can be readily formed as conductive patterns.

[0070]FIG. 4 shows a configuration example of the liquid detectionsection 62. The liquid detection section 62 includes a constant currentsource 62 a, a reference voltage source 62 b, and a comparator 62 c. Oneof inputs of the comparator 62 c is connected to the constant currentsource 62 a and the WET terminal 28. The other input of the comparator62 c is connected to the reference voltage source 62 b. An output of thecomparator 62 c is supplied to a charge/discharge stoppage logic 64.

[0071] When a liquid is detected by the liquid detection section 62, theliquid detection section 62 activates the charge/discharge stoppagelogic 64. As a result, the charge/discharge stoppage logic 64 turns theswitch (SW) 32 to the ON state. Accordingly, the gate voltage of the FET30 goes LOW, and the FET 30 is turned to the OFF state, whereby bothcharging and discharging of the secondary battery 10 are disabled.

[0072] In this way, when a liquid is detected by the liquid detectionsection 62, the charge/discharge stoppage logic 64 controls the FET 30so as to interrupt the charging/discharging of the secondary battery 10.Thus, it is possible to make a user aware of a malfunction or acorrosion of the circuit due to water or an electrolytic solution, etc.,or a problem due to hydrofluoric acid being generated by addition ofwater to an electrolytic solution.

[0073] The interruption of charging/discharging by the charge/dischargestoppage logic 64 is performed prior to the interruption ofcharging/discharging by the system logic 46.

[0074] The secondary battery control circuit 20 further includes avoltage detecting/outputting section 48 that detects the voltage of thesecondary battery 10 and outputs an output signal (O_(V1)-O_(V6))corresponding to the detected voltage. A reference voltage is suppliedfrom the reference voltage generation section 50 to the voltagedetecting/outputting section 48.

[0075]FIG. 5 shows a relationship between ranges for the detectedbattery voltage and the logic levels of the output signalsO_(V1)-O_(V6). In FIG. 5, Vnor denotes a normal state range; Voc denotesan overcharge range; Vocr denotes a discharging only enabling range;Vodr denotes a charging only enabling range; and Vod denotes anoverdischarge range.

[0076] In the case where the detected battery voltage is within thenormal state range Vnor, the system logic 46 sets the charge disablingsignal CD to a H level, and sets the discharge disabling signal DD to aH level.

[0077] In the case where the detected battery voltage is within theovercharge range Voc or the discharging only enabling range Vocr, thesystem logic 46 sets the charge disabling signal CD to a L level.

[0078] In the case where the detected battery voltage is within thecharging only enabling range Vodr or the overdischarge range Vod, thesystem logic 46 sets the discharge disabling signal DD to a L level.

[0079] The charge disabling signal CD and the discharge disabling signalDD are output from the system logic 46, and are supplied to thecharge/discharge control section 42.

[0080] The charge/discharge control section 42 controls the state of theFET 30 based on the charge disabling signal CD and the dischargedisabling signal DD. The interruption of charging/discharging by thesystem logic 46 based on an output from the temperature state outputsection 54 is performed prior to the interruption ofcharging/discharging by the system logic 46 based on an output from thevoltage detecting/outputting section 48.

[0081] Furthermore, in the case where the output signal O_(V6) (FIG. 5)is output from the voltage detecting/outputting section 48, and theoutput signal O_(T5) from the temperature state output section 54 is ata H level, the forced discharge logic 56 is activated. The forceddischarge logic 56 turns a switch (SW) 34 provided between the negative(−) terminal 24 and the B+ terminal 26 to the ON state, whereby thesecondary battery 10 is forcibly discharged.

[0082] In this way, when the voltage detected by the voltagedetecting/outputting section 48 is equal to or greater than apredetermined voltage value (e.g., 4 V), and the temperature detected bythe temperature detection section 52 is equal to or greater than apredetermined temperature (e.g., 35° C.), the secondary battery 10 isdischarged until reaching a predetermined voltage value (e.g., 3.9 V).Such a forced discharge can reduce deterioration in life cycle andswelling of the secondary battery 10 which result from the chargedsecondary battery 10 being in a high temperature condition.

[0083] For example, in the case where the charged secondary battery 10is left in a temperature condition of 35° C. or more, the capacity ofthe battery can be reduced by 20% by performing the above-describedforced discharge process, whereby deterioration in life cycle (thenumber of times that the battery can be used) can be reduced.Furthermore, in the case where the charged secondary battery 10 is leftin a temperature condition of 60° C. or more, the capacity of thebattery can be reduced by 20% by performing the above-described forceddischarge process, whereby swelling of the battery can be prevented.

[0084] It is preferable that either a predetermined voltage value whichis a starting condition for the forced discharge (e.g., 4 V) or apredetermined voltage value which is a canceling condition for theforced discharge (e.g., 4 V) is equal to the overcharge releasingvoltage value Vocr. This is preferred because additional circuitry isnot required for setting these predetermined voltage values to theovercharge releasing voltage value Vocr, and the overcharge releasingvoltage value Vocr is a practically appropriate voltage value.

[0085] These predetermined voltage values can be detected by a singlecircuit having a hysteresis. Accordingly, the number of comparators canbe reduced as compared to a case where a circuit not having a hysteresisis employed to detect a predetermined voltage value.

[0086]FIG. 6 shows a configuration of a portion of a voltagedetecting/outputting section 48 which outputs the output signal O_(V6).

[0087] The output signal O_(V6) is output from a comparator 48 a. To oneof the inputs of the comparator 48 a (negative (−) input), a voltage VB+which is to be input to the voltage detecting/outputting section 48 issupplied. To the other input of the comparator 48 a (positive (+)input), an output of the comparator 48 a is fed back through a resistor48 d. Furthermore, the positive (+) input of the comparator 48 a isconnected to the reference voltage generation section 50 through aresistor 48 b, and connected to ground through a resistor 48 c. Herein,the resistance values of the resistors 48 b, 48 c, and 48 d are R1, R2,and R3, respectively.

[0088] In the case where the voltage VB+ is smaller than a voltage ofthe positive (+) input of the comparator 48 a (reference voltage 48E),the reference voltage 48E is represented by expression (2-1) shownbelow:

(Output of reference voltage generation section 50)×R2/{R1×R3/(R ₁₊R3)+R2}  (2-1)

[0089] In the case where the voltage VB+ is higher than the voltage ofthe positive (+) input of the comparator 48 a (reference voltage 48E),the reference voltage 48E is represented by expression (2-2) shownbelow:

{(Output of reference voltage generation section50)×(R2×R3)/(R2+R3)}/{R2×R3/(R2+R3)+R1}  (2-2)

[0090] In this way, the comparator 48 a can possess a property ofhysteresis by automatically changing the reference voltage 48E based onwhether the voltage VB+ is smaller or higher than the reference voltage48E. Therefore, a predetermined voltage value which is the startingcondition for the forced discharge and a predetermined voltage valuewhich is the canceling condition for the forced discharge can beestablished by using a single comparator 48 a.

[0091] Furthermore, the canceling condition for the forced discharge mayinclude the temperature condition for the secondary battery 10. Forexample, the forced discharge may be cancelled when the voltage of thesecondary battery 10 reaches a predetermined voltage value (e.g., 4 V)and the temperature of the secondary battery 10 reaches a predeterminedtemperature.

[0092] Still further, a resistor 36 provided between the switch (SW) 34and the B+ terminal 26 is generally formed on a semiconductor chip 20 a.However, the resistor 36 may be provided outside the semiconductor chip20 a so that the value of the resistor 36 can be adjusted from theoutside of the semiconductor chip 20 a.

[0093]FIG. 7 is a cross-sectional view that shows a structure in whichthe secondary battery control circuit 20 of the present invention ispositioned in a sealing section 80 of the secondary battery 10. As shownin FIG. 7, the secondary battery control circuit 20 is accommodatedinside the sealing section 80. An explosion-proof space in the sealingsection 80 is considered in a space for accommodating the secondarybattery control circuit 20. This structure is described in JapaneseCo-Pending Application No. 10-323643.

INDUSTRIAL APPLICABILITY

[0094] According to a secondary battery control circuit of the presentinvention, in the case where a temperature detected by a temperaturedetection section is out of a predetermined first temperature range orout of a predetermined second temperature range, charging/discharging ofthe secondary battery is interrupted. This prevents a liquid leakagephenomenon of an electrolytic solution due to the activation of a PTCelement installed in the secondary battery.

[0095] Further, according to a secondary battery control circuit of thepresent invention, in the case where a voltage detected by a voltagedetection section is equal to or greater than a predetermined firstvoltage value, and the temperature detected by a temperature detectionsection is equal to or greater than a predetermined temperature, thesecondary battery is discharged until the voltage of the secondarybattery reaches a predetermined second voltage value which is smallerthan the predetermined first voltage value. By such a forced discharge,deterioration of a life cycle and swelling of the secondary battery dueto the charged secondary battery being in the high temperature conditioncan be prevented.

[0096] Furthermore, according to a secondary battery control circuit ofthe present invention, in the case where the generation of a liquid isdetected by a liquid detection section, charging/discharging of thesecondary battery is interrupted. This allows a user to notice amalfunction or a corrosion of a circuit due to a liquid, such as wateror an electrolytic solution, etc., or a problem caused due tohydrofluoric acid being generated by addition of water to anelectrolytic solution.

1. A secondary battery control circuit comprising: a voltage detectionsection for detecting a voltage of a secondary battery; a temperaturedetection section for detecting a temperature of the secondary battery;and a control section for controlling charging/discharging of thesecondary battery based on a voltage detected by the voltage detectionsection and a temperature detected by the temperature detection section,wherein in a case where the voltage detected by the voltage detectionsection is equal to or greater than a predetermined first voltage value,and the temperature detected by the temperature detection section isequal to or greater than a predetermined temperature, the controlsection discharges the secondary battery until the voltage of thesecondary battery reaches a predetermined second voltage value.
 2. Asecondary battery control circuit according to claim 1, wherein thepredetermined first voltage value and the predetermined second voltagevalue are detected by a single circuit having a hysteresis.
 3. Asecondary battery control circuit according to claim 1, wherein eitherthe predetermined first voltage value or the predetermined secondvoltage value is equal to an overcharge releasing voltage value.
 4. Asecondary battery control circuit according to claim 1, wherein adischarge canceling condition for the secondary battery includes atemperature condition for the secondary battery.
 5. A secondary batterycontrol circuit according to claim 1, wherein the secondary batterycontrol circuit is formed on a single semiconductor chip.
 6. A secondarybattery control circuit according to claim 5, wherein the singlesemiconductor chip is enclosed in a sealing section of the secondarybattery.